The present invention relates to an electronic part including as an active device a semiconductor crystal layer formed by epitaxial growth on a seed crystal substrate, and a method of producing the same. Furthermore, the present invention relates to an image display system including such electronic parts, and a method of manufacturing the same.
In the case of arranging light-emitting devices in a matrix form to assemble an image display system, it has hitherto been practiced to forming the devices directly on a substrate such as in the cases of a liquid crystal display system (LCD) and a plasma display panel (PDP) or to arrange singular LED packages in the case of a light-emitting diode display (LED). For example, in the cases of the image display systems such as LCD and PDP, the devices cannot be separated individually, so that it has been a usual practice to form the devices spaced from each other by the pixel pitch of the image display system, from the beginning of the manufacture process.
On the other hand, in the case of the LED display, it has been practiced to take out the LED chips after dicing, and connect the LED chips individually to external electrodes by bump connection using wire bonding or flip chips, thereby packaging the LED chips. In this case, the LED chips are arranged at the pixel pitch of the image display system before or after the packaging, and the pixel pitch is made to be independent from the pitch at which the devices are produced.
Since the LED (Light-Emitting Diode) as the light-emitting device is expensive, it is possible to lower the cost of the image display system using the LEDs by producing a multiplicity of LED chips from a single sheet of wafer. Namely, where the size of the LED chips is several tens of μm square, as contrasted to about 300 μm square in the related art, and the LED chips are connected to manufacture an image display system, it is possible to reduce the price of the image display system.
Meanwhile, among the individual semiconductor devices such as not only the light-emitting diode but also, for example, laser diode and transistor device, there are some devices in which the overall area of the device must be not less than several times of the active region (for example, not less than 0.2 mm square) although the size of the active region necessary for operation is on the order of μm. This hampers an enhancement of the actual mounting density of the device or a lowering in the cost of the device.
For example, in the case of high-luminance LED, in account of the fact that a luminance of about several cd is obtained at a chip size of about 300 μm square and according to proportional shrinkage, low-luminance LED with a luminance of not more than about several mcd might have an active region (active layer area) of about 10 μm square. However, according to the conventional device structure and conventional mounting method, it is difficult to set the overall size of the device closer to the size of the active region. In the case of laser diode, the active region is in a stripe form with a width of several μm and a length of several hundreds of μm, but in actual mounting, the device size has a width of not less than about 200 μm.
Particularly, in the case of a light-emitting diode or a laser diode that is produced by epitaxial growth of a gallium nitride based crystal on a sapphire substrate, the cathode side (n-type semiconductor layer) and the anode side (p-type semiconductor layer) are sequentially laminated. In this case, since the substrate is an insulating body, two electrodes must be provided on the growth surface side, so that the device size is large due to wire bonding, but the actual area of the active region (active layer) is rather small. Therefore, internal resistance is high due to flow of current in a lateral direction, and several drawbacks such as unfavorable concentration of current are generated.
On the other hand, in the case of a light-emitting diode composed of an aluminum gallium indium phosphide based crystal grown on a gallium arsenide substrate, electrodes can be provided on both sides of the device, but a portion of the light emitted at an active layer is absorbed by the substrate, so that only an external light emission efficiency much lower than an intrinsic internal light emission efficiency can be obtained. In order to solve this problem, a variety of contrivances have been practiced, for example, formation of a semiconductor multilayer film (DBR) for light reflection in the inside, formation of a thick window layer, or a transfer onto a transparent substrate. These contrivances lead to a rise in cost.